British Steam Engine Recognized As First Boulton and Watt with Parallel Motion

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ASME and the Museum

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An 18th century engine, survivor of a 102-year stint in a London brewery and now housed in an Australian museum, has been designated an ASME historic mechanical engineering landmark.

The first Boulton and Watt rotative engine with parallel motion was designated the 19th International Mechanical Engineering Landmark by the American Society of Mechanical Engineers (ASME). During ceremonies on April 17, Dr. L. S. Fletcher, president of the Society, presented a bronze plaque to Dr. Lindsay Sharp, director of the Power House Museum, part of the Sydney Museum of Applied Arts and Sciences, in Australia.

The parallel motion mechanism is the critical element that allowed long-stroke pumping engines to become double-action and thus able to produce rotational motion. Built in 1785 as a single-acting engine, the Boulton and Watt was altered to its present double-acting configuration in 1795.

Museum staff Bill Bannister and Bert Bruin check parts near the 14-foot flywheel of the Boulton and Watt steam engine now in the Museum of Applied Arts and Sciences in Sydney, Australia. Photo courtesy of ASME and the Museum.

Replaced in 1887 by a more compact, higher powered compound steam engine, it was donated to the Museum and shipped to Australia, where it has been on display since 1888. It was once again restored to working condition for its bicentennial last year.

The engine was high technology for its day and more imposing than other mechanical achievements of the time the windmill and the clock. In May of 1797, King George III took Queen Charlotte and their children to inspect the Brewery works, the chief attraction being the engine. Although of modest capacity, it set a good example, and by 1796, 11 other Boulton and Watt engines were at work in London.

With the ever increasing industrial activity of the 18th century, rotational power beyond that derived from animals, water, or wind was desperately needed. New comen atmospheric pumping engines were used for mine drainage and water systems, but the high cost of fuel was limiting. Millwork was dependent upon shaft power, but these engines had inadequate drives. The unlimited industrial application of a rotative engine was recognized by James Watt, an engineer who in 1776 began a partnership with industrialist Matthew Boulton.

The mechanical invention of which Watt was eventually to say he was proudest is the three-bar mechanism. Watt patented his first parallel motion mechanism in 1784, about the time that Samuel Whitbread, a London brewer, had ordered a single-acting, 24-inch cylinder, 6-foot stroke engine. Whitbread's engine was to be rotative, and a drawing (in the Boulton and Watt Collection in Birmingham) dated November 1784 shows a parallel motion, believed to be the first application of that mechanism. The engine is shown laid out with rack and sector hookup, but a three-bar motion was sketched over it. The Whitbread drawing of a few months later shows a refined parallel motion.

The Brewery's engine is 30-feet (9.14 m) tall and has about the same length, with an overall weight of 33 tonnes. Sometime after the 1795 rebuilding, a cast iron beam, 18 feet 4 inches (5.6 m) center to center and weighing about 9.2 tonnes, replaced a wood, probably oak, beam that might have weighed about 1.5 tonnes. Built of cast iron sections, the 14-foot flywheel and its shaft weigh some 8 tonnes. The connecting rod is 18 feet (5.5 m) center to center.

When first installed in London, the single-acting engine did the work of 24 horses, according to records. This probably meant the total number of animals required during a day not a shift, since a conservative calculation leads to about 17 indicated horsepower (12.7 kW) assuming a mean effective pressure of 10 psia (69 kPa) and a speed of 20-21 strokes per minute. After the engine was made double-acting in 1795, the power of its cylinder doubled, to an hip of perhaps 35 (26 kW).

The ASME National Historic Mechanical Engineering Landmarks Program designates regional, national, and international landmarks, each representing a progressive step in the evolution of mechanical engineering. Each is judged by its influence on society and significance in its immediate locale, in the country, or throughout the world. To date, 112 such landmarks have been designated in 29 U.S. states, Puerto Rico, England, France, and now Australia.